Check the text buffer before parsing.

The tokenizer service was attempting to parse non-PowerShell files.
Fixed that. Started the foundation for Go To Definition.
Merge branch 'dev' of https://github.com/adamdriscoll/poshtools into dev
PSM1\PSD1 Fix

Fixed parsing of PSM1 and PSD1 files. Added support for the diff window.
Fixing #54

Suppressing an exception coming that was being thrown when stopping a
script.
Merge branch 'dev' of https://github.com/adamdriscoll/poshtools into dev